Quite by chance, I just saw a map of the States showing the African-American population by county in percentage terms. Counties with fifty percent or more are the darkest while those with five percent or less are the lightest. It is a map of slavery, I realized at once. Even though quite a number of blacks have moved north over the last century, their distribution across the country still reflects the divide that led to the civil war two centuries ago. Several large cities are the only exception. I expected some inertia in the distribution of erstwhile slaves, but I was stunned by its actual strength. The map singles out the three cities where racial unrest has been brewing as of late—Ferguson, Missouri, Cleveland, Ohio, and New York City. They are at the northern tips of black population migrations from the south. At least for the time being, there are no signs of racial unrest in areas with the highest percentages of Afro-Americans. Those who have stayed close to the fields where their ancestors toiled as slaves are apparently at peace. For better or worse, a division of the States along racial lines is out of the question. Intermingling of blacks and whites will take a few millennia. In the meanwhile, slavery of old will keep causing unrest across the country. And it looked like such a clever idea only three or four centuries ago.